(a) Field of the Invention
The present invention relates to a radio frequency identification tag for attaching to metal. More particularly, it relates to a radio frequency identification tag antenna for attaching to metal by using proximity coupling.
The present invention was supported by the IT R&D program of MIC/IITA [2006-S-023-02, Development of Advanced RFID System Technology].
(b) Description of the Related Art
A radio frequency identification (RFID) tag is used in various fields such as distribution and material handling industries together with an RFID reader.
When an object to which the RFID tag is attached accesses a read zone of the RFID reader, the RFID reader transmits an interrogation signal to the RFID tag by modulating an RF signal having a specific carrier frequency and the RFID tag responds to the interrogation of the RFID reader.
That is, the RFID reader transmits an interrogation signal to the RFID tag by modulating a continuous electromagnetic wave having a specific frequency, and the RFID tag transmits back the electromagnetic wave transmitted from the RFID reader after performing back-scattering modulation in order to transmit its own information stored in the RFID tag's internal memory. The back-scattering modulation is a method for transmitting tag information by modulating the amplitude and/or the phase of a scattered electromagnetic wave when the RFID tag transmits the electromagnetic wave that is initially transmitted from the RFID reader back to the RFID reader by scattering the electromagnetic wave.
Since a passive RFID tag does not include a separate operation power source, it rectifies the electromagnetic wave transmitted from the RFID reader and uses the rectified electromagnetic wave as its own power source to acquire operation power. The intensity of the electromagnetic wave transmitted from the RFID reader should be larger than a specific threshold value for normal operation. However, since the transmission power of the reader is limited by local regulations of each country, it is not possible to unconditionally raise the level of transmission power.
Therefore, the RFID tag should efficiently receive the electromagnetic wave transmitted from the RFID reader to extend the read zone without raising the transmission power level of the reader. A method for raising the receiving efficiency of the RFID tag is to perform complex conjugate matching of an RFID tag antenna and a radio frequency (RF) front-end of the RFID tag chip so as to maximize the intensity of the signal received by the RFID tag.
A conventional antenna will be described in detail with reference to FIG. 1.
FIG. 1 is a configuration of a conventional antenna.
As shown in FIG. 1, the conventional antenna 10 includes a first dielectric material layer 11, a second dielectric material layer 13, a microstrip patch 15, and a microstrip line 17.
Both of the first dielectric material layer 11 and the second dielectric material layer 13 have low dielectric constants, and they are formed by accumulation. In this instance, the second dielectric material layer 13 is formed below the first dielectric material layer 11, and a ground surface is formed in a bottom surface of the second dielectric material layer 13.
The microstrip patch 15 is formed in a part of an upper surface of the first dielectric material layer 11, and determines a resonance frequency of the antenna.
The microstrip line 17 is formed in a part of an upper surface of the second dielectric material layer 13.
In design of the conventional antenna 10, the first dielectric material layer 11 and the second dielectric material layer 13 are stacked in order to feed the microstrip patch 15 by way of electromagnetic coupling. Accordingly, the microstrip line 17 and the microstrip patch 15 are excited by way of the electromagnetic coupling.
However, a method for controlling the impedance characteristic of the antenna is not considered in the design of the conventional antenna in FIG. 1.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.